This invention relates to a solid-state light-emitting or electroluminescent device for converting electrical energy to the energy of visible rays.
Various solid-state devices of the type described are coming into use as pilot lamps and in particular as solid-state number and/or letter display panels because of their compactness, high reliability, and moderate cost. Among such known sold-state electroluminescent devices, are semiconductor junction diodes that generally produce red radiation. Although a semiconductor junction diode of a crystal of gallium phosphide including nitrogen impurity is capable of producing green rays to which human eyes are more sensitive compared to red rays, it is difficult to grow these crystals because the high volatility of the phosphor requires a high ambient pressure that balances the high vapor pressure of the phosphor while growing the crystal. In addition, the efficiency of conversion of the electrical energy to visible-ray energy is at most 2 percent with a junction diode for red rays and only 0.1 percent with one for green rays. Among solid-state electroluminescent devices of the type described, a combination of an infrared-emitting electroluminescent diode and a luminescent material excitable in a step-like manner is also known which produces red, green, blue, or other rays in accordance with the choice of the luminescent material. The efficiency of conversion is, howver, only 0.2 percent at most with a combination for red rays, 0.02 percent with a combination for green rays, and even lower with a combination for blue rays in the normal mode of operation.